A team of BBC journalists was beaten and their camera smashed in southern Russia, where they were looking into reports of Russian soldiers killed while on secret deployments near Ukraine.
The three reporters were working in the southern city of Astrakhan when they were "assaulted by unidentified men in a coordinated attack," the BBC said in a statement.
"Our staff were badly beaten, their camera destroyed and then taken," the statement said.
BBC spokesman James Hardy added separately: "All are OK."
"The cameraman is continuing to receive treatment for concussion and other injuries," he added in written remarks.
After the assault the journalists were questioned at a police station.
They later "discovered that recording equipment, which was in their vehicle, at the police station, had been electronically wiped".
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The incident is "clearly part of a coordinated attempt to stop accredited news journalists reporting a legitimate news story," the BBC said, calling for a thorough probe.
Astrakhan police spokesman Pyotr Rusanov told Russian news agencies that authorities had launched an enquiry into a robbery and were looking for assailants.
"This was a disturbing day for us," tweeted one of the reporters, Steve Rosenberg, posting his interview with a woman in Astrakhan region who said her brother Konstantin Kuzmin, a Russian serviceman, was killed after deployment to the Russia-Ukraine border.
According to Russian rights organisation Zabytyi Polk (Forgotten Regiment), Kuzmin was one of many Russian soldiers stationed in Chechnya who was sent to the Rostov region, which borders Ukraine, and then killed under mysterious circumstances.
Russia has enforced a virtual blackout on any information concerning the deployment of regular troops to Ukraine.
According to rights campaigners, at least 200 Russian servicemen might have died in eastern Ukraine where fighting between pro-Russia separatists and Kiev forces has claimed nearly 2,900 lives since April.
The Russian government denies ever sending the army to Ukraine, while separatist leaders have said that Russian soldiers have participated in the fighting while on vacation.
'Spate of attacks' on media
Russian military commanders have told families that their husbands and sons are participating in military drills close to the Ukrainian border but some have admitted in private conversations that soldiers had been sent "outside Russia".
Several journalists covering the story have been attacked or harassed in recent weeks.
Last month Lev Shlosberg, a local opposition lawmaker and journalist in the western city of Pskov was hospitalised with head and eye injuries after an attack by three unidentified men.
Shlosberg was one of the first people to report on the deployment of local paratroopers to Ukraine.
His newspaper Pskovskaya Guberniya said that dozens of Pskov-based soldiers had been killed.
Other Russian journalists investigating reports of soldiers' deaths were also threatened by men near Pskov last month, and had the tyres of their car punctured.
The Organisation for Security and Cooperation in Europe (OSCE), which monitors the Ukraine conflict, condemned the attack on the BBC as "totally unacceptable" calling it only "the latest in a spate of recent attacks against journalists who investigated issues related to the conflict in eastern Ukraine."